This invention relates generally to drag racing equipment and in particular to methods and apparatus for locking the hydraulic braking system on drag racing vehicles.
In the sport of automotive racing, the race is begun by a starting system consisting of a series of lights of various numbers, commonly called “Christmas tree” lights. Typically, there are one to five warning lights of amber color, one green colored light to indicate the start of the race and one red light to indicate a foul start.
Before the Christmas tree is activated, the vehicles must be “staged” into the starting area. This is typically accomplished using a “line lock” device in cooperation with the vehicle's transmission brake. A line lock device typically consists of a solenoid valve that isolates the front brake hydraulic system from the master cylinder. The line lock is activated by a line lock button, usually mounted on the steering wheel, which opens and closes the solenoid, activating the line lock. In use, the vehicle driver presses on the brake pedal to apply the brakes, then engages the line lock to maintain pressure in the front brake circuit after the brake pedal is released. Locking the front brakes in such a manner allows the driver to spin the rear tires to heat them up as well as assisting in staging as discussed hereinafter.
The transmission brake, or transbrake, is a mechanism that selectively places the transmission in first and reverse gears simultaneously, effectively holding the car stationary. It is used on vehicles with automatic transmissions that employ a torque converter, where it is beneficial to build up pressure in the torque converter before the vehicle is launched. The transbrake is activated by the driver activating a solenoid in the transmission. With the transbrake engaged (transmission locked), the engine throttle can be increased to in preparation for launch without the car creeping forward. Milliseconds before the green light illuminates on the Christmas tree the transbrake is released. The power from the engine is then instantly transmitted to the wheels through first gear. This results in extremely quick acceleration of the vehicle.
Typically, a drag race car is staged by engaging the line lock device, then using the transbrake to bump the car into the starting box right before the start. Unfortunately, because the line lock device relies on the driver's foot pressure to set the initial stopping force on the front tires, the brake stopping force may not be consistent from race to race. If the stopping force is too little, the car may creep forward too quickly, leading to a false start. If the stopping force is too much, the car will not creep forward to the starting box and/or momentary release of the transbrake will cause the vehicle suspension to load up, altering the vehicle from its optimum attitude at the start.
Various methods and apparatus have been suggested for improving consistency in the operation of line locks and launch control. Published US Application US 20110175438 discloses a Vehicle Line-Locking Braking System and Method incorporating a computer that performs various status checks before enabling the line locking device. US Patent Application 20140129107 discloses a brake system for a vehicle that includes a wheel hold mode in which the wheel brake pressure is maintained at the wheels of the non-driven axle alternatively by depressing the brake pedal or by engaging the Antilock Brake System (ABS) pump. The prior art solutions add significant complexity with concomitant reduction in reliability.
What is needed, therefore, is a method and apparatus for applying a consistent, repeatable, brake pressure to the front brakes of a vehicle equipped with a line locking device, without adding significant weight or complexity to the brake system.